Spatio-temporal distribution of longline catch per unit effort, sea surface temperature and Atlantic marlin

Abstract

Atlantic blue and white marlin are currently overfished, primarily as a result of bycatch in pelagic longlines directed at other species. One possible management measure to reduce fishing mortality on these species would be to restrict fishing effort in times and places with exceptionally high marlin catch per unit effort (CPUE). The International Commission for the Conservation of Atlantic Tunas maintains a database of catch and catch-effort statistics of participating nations. These data were analysed to determine whether the distribution of CPUE is sufficiently heterogeneous in time and space that such measures might provide meaningful management alternatives. The resulting distributions of catch rates were also contrasted with monthly average sea surface temperatures to examine the possible association between temperature and CPUE. The results show spatio-temporal heterogeneity in catch rates that may be partly explained by seasonal changes in sea surface temperatures. The time–area concentrations of high CPUE differ between the species. This observed heterogeneity might be exploited to develop alternatives for reducing fishing mortality for future management of the fisheries, but additional research is needed to refine the spatial scale of the analysis and to more fully understand the factors contributing to the observed distribution.